Conversion of hydrocarbons



Nov l, 1949. P. M. ARNOLD CONVERSION OF HYDROCARBONS Filed April l, 1946 m5 myn@ mJmmmm INVENTOR.

D m m A. M P L H P m li ATTORNEYS l.: m2 Por 9 .UDOONE @N Pr@ w o mall@ mJmmma N Patented Nov. l, 1949 UNITED STATES PATENT QFFICE CONVERSION F HYDROCARBON S Philip `M. Arnold, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Application April 1, 194s, serai No. 658,727

4 claims. (ci. 19e-55) combustion of fuel gases and the transference of4 the resulting hot pebbles to a second heating or conversion chamber for heating the gases being processed and furnishing the heat of reaction. A continuous stream of hot pebbles is passed thru the conversion chamber by gravity flow and transferred by means of a bucket type elevator (or other lifting c'levice)` to the pebble heater for reheating and recycling thru the system;

In processes which function most advantagesously at extremely hightemperatures, for 'example in the thermal cracking of light hydrocarbons to produce lighter fractions such as acetylene. the pebbles leaving the cracking chamber are still at a very high temperature and can be handled in elevator equipment only if high temperature alloy materials are used. Furthermore, in conventional apparatus it is diicult, if not impractical, to attain the high temperatures that are so advantageous in the cracking of the lighter hydrocarbons to produce acetylene wherein temperatures of 3000 F. to 3500 F. are especially desirable.

It is an object of the present invention to provide arrangements of apparatus and processes which facilitate the attainment of extremely high temperatures in a bble heater.

Another objectv of this invention is to provide improvements in processes for heating hydrocarbon gases to high temperatures for conversion processes. Y

A further object is to obtain a lower pebble temperature in the elevator apparatus so ythat expensive alloy equipment is not` required, without lowering the heating eiciency of the pebble heater type apparatus. Y Y

Other objects and applications of the present inventionA will become apparent in the accompanying description.

In one embodiment of the invention the hot pebbles flowing from the hydrocarbon conversion chamber are passed through a third chamber in intimate contact with a streamof air passing therethru. This step cools the pebbles to a temperature below that above which special vhigh temperature alloys are required in the elevator.

A As a further refinement of this feature of the invention, the hot air emanating from the third chamber, which is both an air-heating chamber and a pebble-cooling chamber, is passed to the iirst or pebble heating chamber where it is utilized to burn fuel for' heating the pebbles.

In another embodiment of the invention a portion of the eilluent hydrocarbon product from the cracking or conversion chamber is passed to the combustion zone as fuell thereby utilizing preheated fuel and attaining a higher temperature for the process than is otherwise attained. This feature is also combined with preheating of the air fed to the combustion fuel in order to obtainf the extremely high temperatures so effective in the pyrolysis of light hydrocarbons for acetylene production. This modification is preferred when the feed is relatively cheap and the concentration of the product in the eiliuent is relatively low. In still another embodiment of the invention the fuel fed to the combustion zone is preheated by indirect heat exchange with the hot eiliuent product from the conversion chamber. This expedient is double-edged'in that hotter pebbles are obtained by preheating the Yfeed and a desirable cooling of the product is obtained. Preheating of the fuel by this method is preferred where the product' being manufactured is too expensive to be used as fuel and where there is a high concentration of the desired product in the eiiiuent gases from the conversion chamber. This invention may also be applied to the-heating of gases such as steam, air,` nitrogen, etc., where high temperature without contamination of the gases is desired. p The term pebble as used throughout the specication denotes any refractory material in rlowable form and size which caribe utilized to carryheat from one zone to IlQther. vPebbles are conventionally substantially vspherical and are from about $4," to about 1"V in diameter with the preferred size for high temperature processes about 1A". Pebbles must be of refractory materials which will withstand temperatures at least as high as 'the highest temperature attained in to 4000 F. are now in use.

' For a more complete understanding of the invention, reference may be had to the accompanying drawing in which Figure l is a diagrammatic showing of apparatus arranged so as to preheat combustion air and cool pebbles before they are transferred into the elevator.

' Figure 2 is a diagrammatic showing of a suitable arrangement of apparatus for preheating the air for fuel combustion and simultaneously feeding preheated fuel, a portion of the product hydrocarbons, to the combustion zone.

Figure 3 shows diagrammatically a preferred arrangement of apparatus for preheating the fuel by indirect heat exchange with the hot eiuent product from the conversion reaction.

In Figure 1, I is an insulated, refractory lined heating chamber for heating iiowable ypebbles of a ceramic or metallic composition; II and I2 are heating chambers of similar construction, the former forheating the gases being processed, the latter for preheating air for aiding the combustion required for heating chamber I0; and I3 is an elevator of the continuous, bucket type for transferring pebbles from chamber I2 to cham- Y' ber III for reheating and 'recycling thru the system. Chambers I0. Il, and I2 are arranged at successively lower levels and connected by conduits I4 and I5 to accommodate the natural now of pebbles through the apparatus. A star wheel I6, or similar device, in conduit I'I controls the rate of ow of pebbles through the -apparatus and feeds the pebbles into conduit I8 leading into elevator I3. Proper screening devices may be inserted in conduit I8 for removing nes and broken pebbleslthrough a closable opening not shown. Pebbles reaching the top of the elevator are dumped into conduit I9 from which they now thru conduit or inlet means 2| into heater I0 for reheating and recycling. Conduit I9 is provided with means not shown for introducing fresh pebbles to the system. Lines 22, 23, and 24 are steam lines for admitting suflicient steam to the connecting conduits to prevent any substantial escape of gas from one chamber to another wherein substantially equal pressures are maintained, these pressures being sub-atmospheric, atmospheric, or superatmospheric as desired.

The hydrocarbon or other gas feed is introduced to heater II through line 25 and the product is removed through line 26. Lines 21 and 28 admit to and remove air from chamber I2, line 28 being connected to line 29 which feeds air via line 3| to furnace 32 connected with pebble heater I0. Line 3| feeds fuel to furnace 32 connected with heater I0 and line 20 carries combustion gas out of heater I0.

Valve 33 in line 29 serves to admit air from any convenient source for tempering purposes or as an independent supply when desired.

In Figure 2 the arrangement. is varied so as to permit the utilization of preheated fuel along with preheated air as in Figure 1. Fuel line 3| is connected to product gas line 26 leading from the hydrocarbon conversion chamber II. Valve 34 in line 26 and valve 35 in line 3| serve to control the proportion of product gas utilized as fuel.

Figure 3 sets forth an arrangement of apparatus which permits the preheating of an independent fuel supply by indirect heat exchange with the hot eiliuent gas from heating chamber II. Heat exchanger 36 is inserted in lines 26 and 3| to eifect the desired preheating of fuel gas owing through line 3|.

.This invention is especially advantageous in the production of acetylene. Light hydrocarbon gases are cracked at a temperature of 1400 to 2000 F. in chamber II of Figure 1 under conditions to produce an abundance of ethylene. The ethylene-containing eiuent from chamber is fed into a second pebble heater apparatus, such as shown in Figures 2 or 3, which involves preheating both the air and fuel in this second system and attains a temperature of from about 3000 to 3500 F. The use of such high temperatures in cracking light hydrocarbons such as ethylene to produce acetylene made attainable by this invention results in a much greater concentration of acetylene in the product gases and a much more economical production of acetylene. The prior art method of producing acetylene at temperatures up to about 3000* F. entails dilution of the product gases with combustion gases, due to direct contact with burning fuels, thereby adding to the cost of recovering acetylene. The present invention makes it possible to produce more acetylene from a given amount of feed and a much higher concentration of acetylene in the product gas. In the production of acetylene by thermal cracking or thermal dehydrogenation of ethylene at high temperatures in a pebble heater, the expedient of utilizing a part of the hot eiiiuent product from the conversion zone for fuel in the combustion zone is especially desirable and makes it possible to attain temperatures up to about 3500 F. in the conversion zone. Such high temperature operation requires the use of the best electric furnace refractories in the hottest areas of the combustion and conversion zones. Pebbles of a correspondingly high quality are likewise essential. It is found that the smaller more dense pebbles stand up best under the more severe conditions of temperature. Pebbles of approximately 1%" to 1A" diameter and relatively high density are more spall resistant and suffer less breakage than larger pebbles; they also have more heating surface for a given volume and hence are more ecient. Pebbles must be sufficiently large and dense to permit high feed ow rates without being suspended or lifted by countercurrent gas flow, the preferred technique.

In operation refractory pebbles ll the three heating chambers I0, II, and I2, and the connecting conduits, their ilow through the system being regulated by operation of star wheel I6 in conduit I1 according to the temperature required in conversion chamber II. Where heating demands are high, more rapid flow of hotter pebbles is required than where they are low. Pebbles are heated in chamber I0 by combustion gases owing therethru from furnace 32 which is supplied fuel from any convenient source through line 3| and preheated air from line 29. The rate of combustion and degree of preheating of the air and/or fuel determine the temperature attained in heater I0. Combustion gases withdrawn through line 20 can be utilized in any desirable manner to recover the sensible heat thereof. Heated pebbles are permitted to flow through chamber at a rate and temperature which insures the maintenance of the desired conversion temperature therein. The higher the temperature differential between pebble temperature and conversion temperature, the slower will be the rate of flow and vice versa. At the higher conversion temperatures, e. g., above 3000" F.. more rapid pebble flow rates are' required, assuming other factors constant.

The gas to be heated or processed is fed into chamber II via line 25 and the hot product is discharged through line 26 after being contacted and heated by the hot pebbles flowing through the chamber. In chamber II the pebbles give up considerable heat to the feed gas but enter chamber I2 via conduit I5 at a temperature often considerably in excess of 1000c F. and are cooled by air being passed through this zone, via lines 21 and 28, so that their high temperature will not result in damage to the elevator equipment. Cooled pebbles leave zone I2 through conduit I1, their iiow being regulated by feeder or star wheel I6, and flow into conduit I8 which allows them to descend to the lower portion of elevator I3. Elevator I3 carries the pebbles to the upper end of conduit I9 where they are dumped and flow therethru into conduit 2| and heater I0.

The ow of air through zone I2 is regulated to provide the desired cooling effect on the pebbles and the extent of preheating of the air advantageous to the degree of heating desired in chamber I0. This preheated air is passed via lines 28, 29 and 3| to furnace 32 for supporting combustion of fuel fed in thru line 3|. It may be tempered with air admitted through valve 33 in line 29. The combustion fuel may be preheated as shown in Figure 3 by passing it through an indirect heat exchanger 36, or it may be taken from line 2B as shown in Figure 2, as a portion of the hot efuent from chamber II, in a case where the gas being processed is a hydrocarbon.

While this invention is particularly advantageous in the production of ethylene and acetylene, it has wide application to thermal cracking and dehydrogenation of the lighter hydrocarbons. It has special utility where rapid heating, careful control of temperature, and high temperatures are demanded. In endothermic reactions requiring rapid transfer of large quantities of heat, the apparatus and method ofthis invention offer their highest utility. An important advantage of the invention is that there is substantially no dilution or contamination of the product gases with combustion gases as there is in directly heating the feed gases by combustion of fuel. Another advantage is the avoidance of frequent interruptions or shutdowns to burn out deposited carbon in the conversion chamber. In the process of the invention, most of the carbon formation is on the pebbles and is extremely light due to the short contact time between the pebbles and the gases being cracked or dehydrogenated.

I claim:

l. A process for the conversion of hydrocarbons which comprises gravitating a contiguous mass of pebbles through a series of superposed zones connected by relatively narrow pebble passageways, including a pebble heating zone, a conversion zone, and a pebble cooling zone in descending order; contacting that section of said mass of pebbles in said pebble heating zone with hot combustion gas so as to heat the same to a temperature above conversion temperature; contacting the resulting hot pebbles in said conversion zone with a stream of hydrocarbon so as to heat and convert the same to desirable product;

contacting that section of pebbles in said pebble cooling zone with a. stream of oxygen-containing gas so as to cool said pebbles and heat said gas; recovering heated oxygen-containing gas and a portion of the hydrocarbon conversion eiuent and forming a combustible mixture thereof; burning said mixture in said pebble heating zone so as to form the combustion gas for the pebble heating step; and recovering converted hydrocarbon.

2. The process of claim 1 in which the conversion process comprises cracking.

3. The process of claim 1 in which the conversion process comprises cracking light hydrocarbons to acetylene.

4. In an apparatus for heating hydrocarbon gases to high temperatures by contact with a stream of hot pebbles, the combination of a flrst heating chamber for heating said pebbles by heat of fuel combustion, supply and discharge conduits leading to and from said rst heating chamber for continuous now of fuel thereto and combustion gas therefrom, a second heating chambei` for heating the hydrocarbon gases being disposed at a lower level than said rst heating chamber, supply and discharge conduits leading to and from said second heating chamber for flow of said gases therethrough, conduit means communicating between the discharge conduit in said second heating chamber and the fuel supply conduit in said rst heating chamber for continually passing a part of the eiiluent hydrocarbon gases from the second heating chamber to the first heating chamber, conduit means in communication with the i'lrst and second heating chambers for gravity ow of pebbles therebetween, a third heating chamber for heating air for fuel combustion in the rst heating chamber being disposed at a lower level than the second heating chamber, supply and discharge conduits leading to and from said third heating chamber for flow of air therethrough, conduit means for continuously passing heated air from the discharge means of the third heating chamber to the supply means of the rst heating chamber for fuel combustion, conduit means in communication with the second and third heating chambers for gravity flow of hot pebbles therebetween, an inlet in the first heating chamber for admitting pebbles, an outlet in the third heating chamber for withdrawing pebbles, and means for transferring pebbles from said outlet to said inlet.

PHILIP M. ARNOLD.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,389,636 Ramseyer Nov. 27, 1945 2,399,450 Ramseyer Apr. 30, 1946 2,405,395 Bahlke et al. Aug. 6, 1946 OTHER REFERENCES Trinks, Industrial Furnaces, 2nd edition, vol. II, page 297, John Wiley 8: Sons, 1942. 

